Roll forming is a widely practiced method of material forming that can be particularly advantageous when producing parts that are formed into a sectional profile characteristic from an extended length of a strip of material, usually thin sheet metal. Forming the bends that make up the characteristic profile on a press brake one at a time is an alternative approach, but is an alternative wrought with the penalty of a significantly longer cycle time per part. The primary disadvantage of roll forming, however, has been the inflexibility associated with not being able to run more than one part with a given tooling set up, and the relatively long change over time between part runs. For this reason, roll forming has in the past been justifiable primarily for complex parts produced at high volumes.
Advances in roll forming machines have generally lessened the otherwise inherent inflexibility of roll forming approaches. Methods of quickly changing the roll forming tooling have been advanced in recognition of the lengthy delays associated with breaking down a setup and reconfiguring it. Typical of these advances include the use of a turret to store a number of forming tools and deliver the desired tool to an operable position, such as according to the teaching of U.S. Pat. No. 4,557,129 issued to Lash et al. Microprocessor-driven systems have been applied to the process to provide quick, automated tool changes, such as in accordance with the teaching of U.S. Pat. No. 5,761,945 issued to Vandenbroucke. Other approaches recognize the value of variable tooling, such as the variable flange width capability according to the teaching of U.S. Pat. No. 5,163,311 issued to McClain et al. Still other known approaches utilize more than one roll forming line sharing a common drive train mechanism.
In some applications the ability to use the same roll forming tooling but at various laterally spacings has been recognized as an advancement in the art. Approaches providing a variable width part, such as according to U.S. Pat. No. 5,187,964 issued to Levy, are particularly well suited to the production of families of parts that have common formed edges separated by a variable medial web. An example is in the production of metal truss components used in the construction industry, where cee purlins and zee purlins are commonly used having various heights as determined by the width of the web.
Further advancement yet was made by making the roll forming tooling convertible, that is, capable of being adjustable so that the flange provided by the tooling can be positioned in a first mode to form the flange generally upwardly, and can furthermore be positioned in a second position whereby the flange is formed generally downwardly. An approach providing such an advancement was recognized in U.S. Pat. No. 4,787,232 issued to Hayes, which teaches a roll forming member that is convertibly adjustable so as to enable the production of either cee or zee purlins.
As the art continues to evolve, advances will be recognized that further simplify and enhance the process of making families of parts on a common tooling arrangement in a roll forming machine. One opportunity for improvement lies in an ability to standardize the roll forming tooling among the sequential passes providing the progressive forming. Hayes and other related teachings rely on the approach of using dedicated tooling to form the associated incrementally formed flange.
For example, a simple ninety-degree angle is commonly formed in a number of passes, each of which urges the flange incrementally toward the ultimate ninety degree angle. In forming a quality bend the amount of bending per pass is obviously limited. In forming the ninety degree angle a typical approach would be to do so in six passes of approximately 15 degrees in each pass. The roll forming tooling of the prior art thereby consists of six different sets of rollers, typically a matching male and female roller, that contain the roll forming edges which incrementally form the flange. It would be advantageous, in terms of reduced complexity and expense, to provide for all the passes to utilize common roll forming tooling and incorporate the incremental forming in another manner, such as the manner in which the tooling is supported.
Another opportunity for improvement lies in providing the ability to form materials having coatings that cannot be disrupted by the forming process. Galvanized steel, for instance, is susceptible to premature corrosion when the base metal is exposed from marring or cracking of the zinc coating. Prepainted steel is another example of coated material not well suited for roll forming in the current state of the art.
The reason that coated materials are not well suited to roll forming lies in the nature of conventional roll former tooling approaches, wherein a female roller is pressingly engaged by a male roller, both defining the desired profile of the part after passing thereby. This arrangement inevitably provides a roller-to-part engagement with varying roller velocities across the formed portion of the part. This results in a wiping action between the roller and the part, which is likely to damage the coating on a coated part.
It would be advantageous to provide a roller to part engagement interface such that the velocity of the roller contact surface is constant across the formed portion, thereby preventing surface damage to the part during forming.
There is a need in the industry for an advancement in the art that would satisfy these and other related requirements, making the roll forming approach viable in a broader scope of uses as a simpler and less expensive alternative in comparison to other well known metal forming approaches.